Amorphous (non crystalline) oxide semiconductors for use in TFTs have higher carrier mobility and larger optical band gaps and can be deposited at lower temperatures as compared with general amorphous silicon (a-Si). Therefore, the amorphous oxide semiconductors are expected to be applied to next-generation displays which are required to have large sizes and high resolutions and to achieve high-speed drive; and to resin substrates which have low thermal stability. As compositions of oxide semiconductors suitable for these applications, In-containing amorphous oxide semiconductors have been proposed. For example, In—Ga—Zn-based oxide semiconductors, In—Ga—Zn—Sn-based oxide semiconductors, In—Ga—Sn-based oxide semiconductors and the like have been attracting attention.
For formation of a thin film of the above oxide semiconductor, a sputtering method has been preferably employed, in which a sputtering target (hereinafter sometimes referred to as a “target material”) of the same material as the thin film is subjected to sputtering. The sputtering target is used in a state where an oxide sintered body is bonded to a backing plate. However, the oxide sintered body has sometimes been cracked in a step of bonding the oxide sintered body to the backing plate.
For example, Patent Document 1 discloses an oxide semiconductor film suitable for a patterning step in preparing a semiconductor device, and an oxide sintered body containing indium element (In), gallium element (Ga) and tin element (Sn) in atomic ratios of 0.10≤In/(In+Ga+Sn)≤0.60, 0.10≤Ga/(In+Ga+Sn)≤0.55 and 0.0001≤Sn/(In+Ga+Sn)≤0.60, as an oxide sintered body which can deposit the above semiconductor film.
Patent Document 2 discloses an oxide sintered body containing indium element (In), gallium element (Ga), zinc element (Zn) and tin element (Sn), and containing a compound represented by Ga2In6Sn2O16 or (Ga,In)2O3, as a technique for reducing abnormal discharge during sputtering.
Moreover, Patent Document 3 discloses a sputtering target which is excellent in sputtering operability such as an increase in sputter rate, prevention of the occurrence of nodules and prevention of cracking, and possible to form a transparent conductive film particularly low in resistance in a low-temperature substrate; and a high density ITO sintered body having a sintered density of 90% or more and 100% or less and a sintered grain size of 1 μm or more and 20 μm or less, as an ITO sintered body for use in a target material.